In view of the more stringent environmental-pollution guidelines that are being implemented, the sensor system for detecting combustion engines' exhaust gases is becoming increasingly important. In this context, gas sensors based on solid electrolyte are often used, which identify the gaseous components to be detected in the exhaust gas in a highly selective manner. A special challenge in this context is the determination of concentrations, e.g., of oxidizable exhaust gas components, especially in cases where the relevant internal combustion engine is operated under oxygen-rich conditions. One example of this challenge is the identification of hydrocarbons or ammonia in exhaust gases of internal combustion engines that are operated with a surplus of oxygen.
Published European patent document EP 678 740 describes a gas sensor based on solid electrolyte, which is used to identify nitrogen oxides. The measuring principle of the sensor is based on removing excess oxygen within the gas sensor without changing the concentration of nitrogen oxide and, following the formation of a constant low oxygen atmosphere, amperometrically ascertaining the concentration of nitrogen oxides. This sensor can also be used, inter alia, for determining the concentration of hydrogen or ammonia. For this purpose, however, the sensor must feature a proton-conducting solid electrolyte layer, the installation of which layer is expensive and the durability of which layer is limited.
An object of the present invention is to provide a method and a sensor element for a gas sensor which reliably and cost-effectively provide the determination of a gas in a gas mixture.